Method and apparatus for directed device placement in the cerebral ventricles or other intracranial targets

ABSTRACT

Apparatus for directed cranial access to a site includes a guidepiece and a receptacle. The receptacle includes a lower part having a rim and a base, and a hollow stem at the base adapted to be mounted in a hole in the skull; and an upper part having a rim and an opening at the top. Each part of the receptacle has an interior spherical surface, and they can be joined at the rims to form an inner surface enclosing a spherical interior. The guidepiece includes a body having a spherical outer surface and a cylindrical bore through the center, defining an alignment axis; and a guide tube in the bore. The guidepiece is dimensioned to fit rotatably within the receptacle interior, and the apparatus is assembled by joining the receptacle over the guidepiece body, with the guide tube projecting through the top opening. The guide tube is dimensioned to accept an imaging device such as an ultrasound probe during an imaging stage, and an adaptor is provided, dimensioned to accept a device to be placed at the site during a placement stage. The probe is inserted into the guide tube and the guidepiece is swiveled until the image shows that the alignment axis is aligned along an optimal trajectory to the site, the receptacle is tightened to lock the guidepiece, and the imaging device is withdrawn. Then the adaptor is inserted into the guide tube, and the device is inserted through the adaptor along the established trajectory to the site. After placement of the device into the intracranial target, the adaptor, guidepiece, and receptacle are removed as a unit over the device while the device is held in place.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of and claims the benefit of U.S.patent application Ser. No. 12/479,255, by Alexander C. Flint, titled“Method and apparatus for directed device placement in the cerebralventricles or other intracranial targets”, which was filed Jun. 5, 2009,and which claimed the benefit of Alexander Calhoun Flint U.S.Provisional Application No. 61/059,371, titled “Catheterization of thecerebral ventricles by an ultrasound-aligned guidance system”, which wasfiled Jun. 6, 2008. Each of the said applications is incorporated hereinby reference.

BACKGROUND

1. Field of the Invention

This invention relates to intracranial access. Generally, this inventionrelates to using imagery to establish a trajectory and distance forintroduction of a device to a site in the brain and, more particularly,to directed placement of a device to the cerebral ventricles.

2. Description of Related Art

Features in and around the brain (the intracranial contents) may beaccessed for diagnosis or treatment by way of a hole drilled through theskull. Accessing the intracranial contents may include introducing adevice, such as a catheter or needle, through the hole to a particularsite.

It may be necessary to place the device with some degree of accuracy.Particularly, where it is desired to place the tip of a device such as acatheter or a cerebrospinal fluid shunt or a needle into a cerebralventricle, accurate placement of the tip of the device is necessary.

Accurate intracranial placement of devices is challenging.Conventionally, the placement at the desired position (the target) maybe approximated by making the hole in the skull at one of the knownlandmark locations on the skull, and then introducing the device throughthe hole in a direction and to a depth that the surgeon estimates willlocate the device tip at the target. Stated another way, theconventional approach, representing a current standard of practice, isessentially “blind”, entailing some degree of guesswork, and as a resultthe placement is not always satisfactorily accurate. Misplaced devicesmay be ineffective, and may result in harm to the patient. Accordingly,it may be necessary to remove and reintroduce an inaccurately placeddevice one or more additional times, until placement is deemedsatisfactory. Repeated placement efforts increase risks of injury ortrauma to the patient, such as bleeding or damage to brain tissue orinfection.

Ventricular catheters and ventricular shunts are typically left in placefor some time following emplacement, with the distal tip at the targetand the proximal end outside the cranium. A ventricular catheter mayserve as a drain, for example, to control flow of fluid from theventricles; or, a catheter may serve as a conduit for introduction of adiagnostic or therapeutic substance to the target. The proximal end ofthe catheter may be connected to a reservoir, from which fluid (such ascerebrospinal fluid) may be removed or into which a therapeutic ordiagnostic substance may be introduced. It is preferred to limitmovement or play in the location of the device at the hole, to preventdisplacement from the target after placement. Accordingly, where thedevice is to be left in place, it is desirable to employ a small hole inthe skull, and typically the hole in the skull for a device that is leftin place for some time has a diameter only a few millimeters larger thanthe diameter of the device.

Various stereotactic guidance systems have been proposed to improvetargeting of intracranial sites; these generally must be deployed in anoperating theater.

In one approach to directed placement of a catheter, the catheter itselfis provided with ultrasound capability. Schultz-Stubner U.S. PatentPublication No. 2007/0083100, for example, describes an ultrasound probeassociated with the distal end of a ventriculostomy catheter, operableto provide ultrasound imaging during advancement of the catheter or whenthe catheter is positioned at a desired location in a cerebralventricle. Gilbert U.S. Pat. No. 5,690,117 describes an intracranialcatheter having a stylet provided with fiberoptics and an ultrasoundtransducer. Ultrasound probes typically produce a beam that is the samesize as the probe cross section, or only slightly larger, and theminiaturized ultrasound probes in these devices are too small to providean interpretable image that would be deep enough and broad enough tovisualize a target and distinguish it from surrounding tissues.Moreover, the imaging parts of these devices are very costly, and thedevices are not likely to be reusable, so they are too expensive to beaccepted.

Boner et al. U.S. Pat. No. 4,681,103 describes a stereotactic guide forobtaining needle biopsies from the brain. It includes a mountingassembly that is screwed into a burr hole in the patient's skull, and aswivel ball disposed in the assembly, and a locking ring disposed overthe swivel ball, which can be reversibly tightened to fix the swivelball in place or loosened to allow it to swivel. The swivel ballconstitutes a socket that receives an intraoperative ultrasound probe,which can be removed and replaced with a needle guide. The “probe is asclose to the brain as possible”, and is shown as projecting into thehole until it is at or below the level of the dura (that is, at or belowthe inner table of the skull). Accordingly, the burr hole must be varylarge, to accommodate these features. The biopsy needle is insertedthrough the needle guide, the biopsy is taken, and the needle isremoved.

SUMMARY

Generally, in various embodiments, apparatus for directed cranial accessto a site includes a guidepiece and a receptacle. The receptacleincludes a lower part and an upper part. The lower receptacle part has arim and a base, and a hollow stem at the base adapted to be mounted in ahole in the skull. The upper receptacle part has a rim and an opening atthe top. Each part of the receptacle has an interior spherical surface,and the parts can be joined at the rims to form an inner surfaceenclosing a generally spherical interior. The guidepiece includes a bodyhaving a spherical outer surface and a lumen through the center,defining an alignment axis. The guidepiece may further include a borethrough the center thereof, and a guide tube in the bore, and in suchembodiments the lumen of the guide tube constitutes the guidepiecelumen. Where a guide tube is present, it may project away from, or mayend flush with, the guidepiece body surface. The guidepiece isdimensioned to fit rotatably within the receptacle interior, and theapparatus is assembled by joining the receptacle over the guidepiecebody, so that the insertion end of the guidepiece lumen is situated atthe top opening; or, where a guide tube is present and projects from theguidepiece body, so that the insertion end of the guide tube projectsthrough the top opening. The guidepiece lumen (or, where a guide tube ispresent, the guide tube lumen) is dimensioned to accept an imagingdevice such as an ultrasound probe during an imaging stage; and toaccept an adaptor is provided, dimensioned to accept a device to beplaced at the site during a placement stage. An optimum trajectory tothe site is established by inserting the probe into the guidepiece(guide tube) lumen to present an image, swiveling the guidepiece untilthe image shows that the alignment axis is aligned along an optimaltrajectory to the site, and tightening the receptacle to lock theguidepiece and establish the trajectory. The distance along thetrajectory to the site is determined with reference to the image. Theprobe is withdrawn from the guidepiece (guide tube) lumen and theadaptor is inserted into the guidepiece (guide tube) lumen, and thedevice is inserted through the adaptor over the determined distancealong the established trajectory to the site. Thereafter the apparatuscan be withdrawn, leaving the device at the site.

Accordingly, in embodiments of one general aspect the invention featuresapparatus for directed cranial access to a site, including a guidepieceand a receptacle; the receptacle includes a lower part and an upperpart, the lower receptacle part having a rim and a base and a hollowstem at the base adapted to be mounted in a hole in the skull, and theupper receptacle part having a rim and an opening at the top, each partof the receptacle having an interior spherical surface, and the upperand lower receptacle parts can be joined at the rims to form an innersurface enclosing a generally spherical interior; and the guidepieceincludes a body having a spherical outer surface and a lumen through thecenter, defining an alignment axis; the guidepiece is dimensioned to fitrotatably within the receptacle interior, and the apparatus is assembledby joining the receptacle parts over the guidepiece body, with thealignment axis projecting from the insertion end of the guidepiece lumenthrough the top opening; the guidepiece lumen is configured anddimensioned to accept an imaging device.

A “spherical” surface, as that term is employed herein, means andincludes a surface that constitutes part of a sphere; and a “spherical”surface, as that term is used herein, further includes an interruptedsurface.

In some embodiments the guidepiece body further includes a bore throughthe center thereof, and a guide tube in the bore, wherein a lumen in theguide tube constitutes the guidepiece lumen.

In some embodiments the apparatus further includes an adaptor insertablewithin the guide tube including an adaptor bore configured anddimensioned to accept a device to be placed at the site. In some suchembodiments the axis defined by the adaptor bore coincides with thealignment axis of the guidepiece; the adaptor bore may be cylindrical,having a diameter about the same as, or slightly larger than thediameter of the device to be placed at the site.

In embodiments of another general aspect the invention features a methodfor placing a device at an intracranial site, by: forming a hole in theskull; assembling the apparatus as described above and mounting theapparatus in the skull; inserting an imaging device into the guidepiece(guide tube) lumen and activating imaging apparatus associated with theimaging device to generate an image of the intracranial contents;swiveling the guidepiece until the image shows that the alignment axisis aligned along an optimal trajectory to the site, and tightening thereceptacle to lock the guidepiece and establish the trajectory;determining the distance along the trajectory to the site with referenceto the image; withdrawing the probe from the guidepiece (guide tube)lumen; inserting an adaptor as described above into the guidepiece(guide tube) lumen; inserting the device through the adaptor bore overthe determined distance along the established trajectory to the site;and withdrawing the apparatus, leaving the device in place at the site.

In some embodiments the device is marked with depth indicia to aid ininserting the device over the determined distance to the target. In someembodiments, for example, a mark may be located at a point that isaligned with the insertion end of the adaptor when the device tip is atthe position where the end of the probe had been; an accurate insertiondistance can be measured in a proximal direction along the device, andthe device is inserted to that point. In some embodiments, for example,marks may be located at intervals along the device length. In someembodiments these marking approaches may be combined.

The invention provides for improved patient safety in intracranialdevice placement, by improving the accuracy of device placement and byreducing or eliminating the necessity to make repeated placementattempts. Risks associated with conventional “blind” approaches, orapproaches requiring estimation or guess work, are mitigated.

The invention provides for orienting an imaging device (such as anultrasound probe) on an alignment axis along an optimal placementtrajectory to toward an intracranial target, and for determination of adevice insertion distance; for fixing the alignment axis; and forinserting a device across the fixed alignment axis over the determineddistance to the target.

According to some aspects of the invention the hole in the skull has adiameter suitable for placement of devices that are to be left in place,and can be made using a twist drill, for example, not requiringelectrical power. The procedure can be conducted outside the operatingtheater. Moreover, the small hole is of a diameter suitable forplacement of a device (such as a catheter or the like) that is to beleft in place for an extended time (typical of a ventriculostomy, forexample).

The invention provides for directed placement of devices to intracranialtargets that are not readily accessible using a conventional blindapproach. For example, devices (such as catheters, for example) may beaccurately placed in specified parts of the ventricular system (such as,for example, the temporal horn of the lateral ventricle) or otherintracranial targets. Because according to the invention the deviceinsertion trajectory can be at an angle with respect to the axis of thehole in the skull (that is, the trajectory can be significantly off theaxis of the hole in the skull), it is not necessary that the hole belocated at a point overlying the target; as a result, a trajectory tothe target that avoids critical brain tissues can be established.

The guidepiece according to some embodiments of the invention can beemployed with any imaging device having any of a range of shapes andsizes, to locate an optimal insertion trajectory to an intracranialtarget, and can be locked in place to establish the insertion trajectoryto the target; and then, by use of an adaptor where necessary, the sameguidepiece, locked in place, can be employed to insert any of a varietyof devices, having any of a range of shapes and sizes, along the sametrajectory to the target.

Following directed placement of a device to the target, the apparatuscan be removed, leaving the device in place substantially undisturbed.

The method of the invention employs many tools familiar to practitioners(standard drill and bit, catheter or other device, etc.), and can bereadily adapted to current practice with very small modification and aneasy learning curve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic sketch in an elevational view showing aguidepiece according to an embodiment of the invention.

FIG. 1B is a diagrammatic sketch showing a guidepiece according to anembodiment of the invention, in a sectional view in an equatorial plane(as indicated at B-B in FIG. 1A).

FIG. 2 is a diagrammatic sketch showing a lower (cup) part of aguidepiece receptacle according to an embodiment of the invention, in anelevational view.

FIG. 3 is a diagrammatic sketch showing an upper (cover) part of aguidepiece receptacle according to an embodiment of the invention, in anelevational view.

FIGS. 4A and 4B are diagrammatic sketches showing stages in assemblingcranial access apparatus according to an embodiment of the invention, inan elevational view.

FIGS. 5A, 5B, 5C are diagrammatic sketches illustrating variousorientations of a guidepiece in a receptacle according to an embodimentof the invention, in a sectional view thru an alignment axis.

FIGS. 6A, 6B, 6C are diagrammatic sketches illustrating variousorientations of a guidepiece in a receptacle according to an embodimentof the invention, in a plan view.

FIGS. 7A-7D are diagrammatic sketches in sectional view showing stagesin mounting cranial access apparatus according to an embodiment of theinvention.

FIGS. 8A and 8B are diagrammatic sketches in sectional view showingdeployment and operation of an ultrasound imaging device in cranialaccess apparatus according to an embodiment of the invention.

FIG. 9 is a diagrammatic sketch showing display of an image obtained byoperation of an ultrasound imaging device as shown in FIG. 8B.

FIGS. 10A, 10B, 11A, 11B, 12A, 12B are diagrammatic sketches showingguidepiece adaptors according to examples of embodiments of theinvention. FIGS. 10A, 11A, 12A are in three-dimensional view and FIGS.10B, 11B, 12B are in sectional view as indicated at B-B thru FIGS. 10A,11A, 12A, respectively.

FIG. 13 is a diagrammatic sketch in three-dimensional view showingcranial access apparatus, according to an embodiment of the invention.

FIGS. 14A-14E are diagrammatic sketches in sectional view showingdeployment of an intracranial catheter using cranial access apparatus,according to an embodiment of the invention.

FIG. 15 is a diagrammatic sketch in a sectional view illustrating anintracranial catheter secured at the scalp.

FIGS. 16A, 16B, 17A, 17B are diagrammatic sketches showing variousguidepiece adaptor configurations according to examples of embodimentsof the invention. FIGS. 16A, 17A are in three-dimensional view and FIGS.16B, 17B, are in sectional view as indicated at B-B thru FIGS. 16A, 17A,respectively.

FIG. 18 is a diagrammatic sketch in three-dimensional view showingcranial access apparatus, according to an embodiment of the invention.

FIGS. 19A, 19B, 20A, 20B, 21A, 21B are diagrammatic sketches inthree-dimensional view showing cranial access apparatus according to anembodiment of the invention.

FIGS. 19A, 20A, 21A are in three-dimensional view and FIGS. 19B, 20B,21B are in sectional view in an equatorial plane as indicated at B-Bthru FIGS. 19A, 20A, 21A, respectively.

FIG. 22A is a diagrammatic sketch in a sectional view showing cranialaccess apparatus according to another embodiment of the invention.

FIG. 22B is a diagrammatic sketch showing display of an image obtainedby operation of an ultrasound imaging device as shown in FIG. 22A.

FIG. 23A is a diagrammatic sketch in a sectional view showing cranialaccess apparatus according to another embodiment of the invention.

FIG. 23B is a diagrammatic sketch showing display of an image obtainedby operation of an ultrasound imaging device as shown in FIG. 23A.

FIG. 23C is a diagrammatic sketch in sectional view showing deploymentof an intracranial catheter using cranial access apparatus, according toan embodiment of the invention as shown in FIG. 23A.

DETAILED DESCRIPTION

The invention will now be described in further detail by reference tothe drawings, which illustrate alternative embodiments of the invention.The drawings are diagrammatic, showing features of the invention andtheir relation to other features and structures, and are not made toscale. For improved clarity of presentation, in the FIGs. illustratingembodiments of the invention, features corresponding to features shownin other drawings are not all particularly renumbered, although they areall readily identifiable in all the FIGs.

In various embodiments, cranial access apparatus includes a guidepiecemounted in a receptacle. The receptacle includes a lower part (cup) andan upper part (cover). The guidepiece includes a body having the form ofa ball having a bore through the center, and a guide tube in the bore.In some embodiments the guide tube projects from the body, constitutinga receiving end of the guidepiece. The parts of the receptacle areconfigured so that when the apparatus is assembled their inner surfacesconform generally to the surface of the guidepiece body. The base of thereceptacle cup has a port that opens through a hollow stem. Thereceptacle stem is configured and dimensioned for insertion into a holein the skull of the subject being treated. The cover has an opening atthe top, to accommodate the projecting guide tube at the receiving endof the guidepiece when the apparatus is assembled.

An embodiment of a guidepiece is shown at 10 in FIGS. 1A and 1B. Theguidepiece body is a ball 12, that is, it has a generally sphericalouter surface 13. A cylindrical bore through the center of the balldefines a cylindrical inner surface 11 and an alignment axis A. A guidetube 16 in the bore has an outer surface 17 and an inner surface 15defining a guide tube lumen 19. In the embodiment shown here a portionof the guide tube projects from the guidepiece body, constituting areceiving end into which a device can be deployed, as indicated by arrow18. In the embodiment shown here the end of the guidepiece tube oppositethe receiving end is generally flush with the body surface. Theguidepiece may be constructed of any of a variety of materials,including plastics, metals, and ceramics, for example, and may includecombinations of materials, and suitable materials may preferably besterilizable. For instance, the guidepiece may be formed substantiallyof one selected material, coated or plated with another selectedmaterial. The guidepiece body and tube may be made of the same or ofdifferent materials. The guidepiece body and tube may be formed in asingle piece, for example by casting or molding. Or, alternatively, thetube and body may be made as separate parts, and the guidepiece may beassembled by inserting the tube into the bore in the body; the tube maybe affixed in the body using an adhesive, for example, or the tube maybe press-fitted in the body.

Embodiments of receptacle parts configured and dimensioned to receivethe guidepiece of FIGS. 1A and 1B are shown in FIGS. 2 (lower, cup part)and 3 (upper, cover part). Referring to FIG. 2, the lower part 20 inthis embodiment has the form generally of a cup 22 having a rim 35 and abase and having a hollow stem 27 at the base. An inner surface 23 of thecup 22 is generally spherical, enclosing an interior 29 that has adiameter about the same as the diameter of the corresponding guidepiecebody. The inner surface 25 of the stem 27 defines a receptacle axisA_(R) and encloses a stem lumen that communicates through a port at thebase of the cup with the interior 29. The outer surface of the stem isat least partly threaded, as indicated at 26. The rim 35 of the cup issituated in a plane generally perpendicular to the receptacle axisA_(R), which runs through the geometric center of the spherical cupsurface 23 and through the geometric axis of the stem lumen. Referringnow to FIG. 3, the upper part 30 in this embodiment has the formgenerally of a cover 32 having a rim 37, and an opening 34 at the top.An inner surface 33 of the cover 32 is generally spherical, enclosing aninterior 39 that has a diameter about the same as the diameter of thecorresponding guidepiece body. The rim 37 of the cover is situated in aplane generally perpendicular to the receptacle axis A_(R), which runsthrough the geometric center of the spherical cover surface 33 andthrough the center of the opening 34. The rims 35, 37 are threadedcomplementarily so that the cover and the cup can be screwed together;in the example shown the cover has “male” threading and the cup has“female” threading. In the example shown the lower receptacle part 20and the upper receptacle part 30 are provided with “wings” 34, 34′ and36, 36′ to aid the user in manually turning the cup stem into a hole inthe subject's skull, and to aid the user in manually turning the cup andcover in relation to one another, about the receptacle axis A_(R). Thereceptacle may be constructed of any of a variety of materials,including plastics, metals, and ceramics, for example, and may includecombinations of materials. For instance, parts of the receptacle mayvariously be formed substantially of one selected material, coated orplated with another selected material. The upper and lower parts of thereceptacle may be made of the same or of different materials; and thestem and cup of the lower part may be made of the same or of differentmaterials, and suitable materials may preferably be sterilizable. Thestem and cup of the lower part may be formed in a single piece, forexample by casting or molding. Or, alternatively, the stem and cup ofthe lower part may be made as separate parts, and the lower part may beassembled by inserting an end of the stem into an opening in the cup;the stem may be affixed in the cup using an adhesive, for example, orthe stem may be press-fitted in the body, for example. The threadedportion of the stem should be of a sufficiently hard material, and thethreads should be sufficiently sharp, so that the stem self-taps intothe hole in the skull. Accordingly, any of a variety of metals or hightemperature ceramics may be particularly suitable, but any of a varietyof suitably hard plastics may also be suitable.

Generally, the respective surfaces of the receptacle and of theguidepiece body are configured to provide for rotation of the guidepiecebody within the receptacle, generally about the geometric center of theguidepiece body. Accordingly the diameter of the outer surface of theguidepiece body is preferably about the same as, or less (by a narrowtolerance) than, the diameter of the inner surface of the receptacle.Generally, for example, the outer diameter of the ball can be the sameas the inner diameter of the fully assembled and fully screwed togetherupper and lower receptacle parts, so that as the upper and lower piecesare screwed together, the ball is locked in place before the parts arefully screwed together. The inner surface of one or both of thereceptacle parts and/or the outer surface of the guidepiece body may bemore or less smooth or, alternatively, the outer surface of the balland/or the inner surface of one or both of the upper and lower parts canbe made finely bumped, ridged, or frosted to increase the coefficient offriction between the surfaces.

A “spherical” surface, as that term is employed herein, means andincludes a surface that constitutes part of a sphere. For example in theembodiments shown in the drawings the guidepiece body constitutes a ballintersected by a cylinder whose axis passes through the center of theball. The intersection of the cylinder and the ball describes twocircles describing two spherical caps and, accordingly, the “spherical”outer surface of the guidepiece body constitutes a sphere lackingspherical caps at opposite poles. Similarly, for example, in theembodiments shown in the drawings the “spherical” inner surface of eachreceptacle part constitutes a part of a sphere formed by intersecting asphere by two parallel planes, one near the equator (defining a rim) andthe other near a pole (defining an opening to the stem lumen in thelower receptacle part; defining the opening at the top in the upperreceptacle part).

In the examples shown in the FIGs the surfaces are shown as beingcontinuous within the boundaries described by the intersecting planes. A“spherical” surface, as that term is used herein, need not becontinuous, and the term further includes an interrupted surface. Forexample, the “spherical” outer surface of the guidepiece body mayconstitute a part of a sphere that may be interrupted by grooves ordimples or other features in the outer portion of the ball. And, forexample, the “spherical” inner surface of either (or both) thereceptacle parts may constitute a part of a sphere that may beinterrupted by grooves or dimples or other features in the inner wall.

A suitable guidepiece body diameter can be within a broad range. Thebody must be sufficiently large to accommodate a probe within the guidetube. The guidepiece rotates (swivels) about the spherical center of theguidepiece body and, as may be appreciated by inspection of thedrawings, a greater viewing range may be obtained if the center of theguidepiece body is as close as is practicable to the outer table of theskull. That is, it may be desirable for the guidepiece body (and thecorresponding receptacle surfaces) to have a smaller diameter. Asdiscussed below, the inner diameter of the stem (and, accordingly, thediameter of the drill hole in the skull) may according to the inventionbe kept small as the size of the guidepiece body and receptacle cup andcover are made larger.

In the embodiments shown in the FIGs., the walls of the cup and thecover are generally uniformly thick, so that the outer surface of thecover and cup are generally spherical. The outer surfaces may have othershapes. For example, the outer surfaces may have a generally polygonal(for example, hexagonal) shape in a transverse sectional view. In suchembodiments the user may be able to grip the cup and cover securelyenough so that the “wings” are not required, and may be omitted.Similarly, any irregularity in the outer surfaces of the cup and cover(for example, ribs or knurling) may provide for a secure grip and, inthis respect the “wings” may be described as a form of irregularity inthe outer surfaces of the cup and cover, respectively.

Assembly of the cranial access apparatus is illustrated, in sectionalviews along the receptacle axis, in two stages at FIGS. 4A and 4B. Theguidepiece 10 is nested into the cup 20 with the projecting part of theguide tube 16 directed generally away from the cup, as shown in FIG. 4A.Because the spherical surface 13 of the guidepiece body has a diameterapproximately the same as (or slightly less than) the diameter of thespherical inner surface 23 of the cup 20, the guidepiece can swivelabout its geometric center within the cup. The cover and the cup arealigned along the receptacle axis A_(R) and the cover and cup are movedtoward one another (as suggested by the arrow) so that their respectivethreaded rims 37, 35 meet, and the projecting part of the guide tube 16passes through the opening 34 in the cover. Once the threads engage, thecup and cover are screwed together by rotating them to one another aboutthe receptacle axis A_(R) to mate the threads. (The “wings” 36, 36′ areshown in the FIGs. as being aligned with the “wings” 34, 34′; they willof course move out of alignment as the cover and cup are screwedtogether.) As the mating proceeds, geometric centers of the sphericalinner surfaces 33, 23 approach one another and eventually coincide. Asnoted above, in some embodiments the spherical surface 13 of theguidepiece body may have a diameter approximately the same as thediameter of the spherical inner surfaces 33, 23 of the cup 30 and cover20, and in other embodiments the spherical surface 13 of the guidepiecebody may have a diameter slightly less than the diameter of thespherical inner surfaces of the cup 30 and cover 20.

In embodiments in which the spherical surface 13 of the guidepiece bodyhas a diameter the same as the diameter of the spherical inner surfaces33, 23 of the cup 30 and cover 20, when the spherical centers coincidethe contact of the receptacle and the guidepiece body can inhibitmovement of the guidepiece swivel about its geometric center within thecup. On the other hand, in embodiments in which the spherical surface 13of the guidepiece body has a diameter slightly less than the diameter ofthe spherical inner surface 33 of the cup 30, the guidepiece can whenthe spherical centers coincide swivel about its geometric center withinthe cup. The respective rims of the cover and cup can be dimensioned sothat they may be advanced further together (that is, for example, thethreads may not be turned to their limit when the spherical centers ofthe receptacle parts coincide), so that even in embodiments where theguidepiece body diameter is smaller than the diameters of the innersurfaces of the receptacle parts, the receptacle can be tightened sothat the parts press inwardly against the guidepiece body and inhibitthe guidepiece form swiveling. A resulting assembly is shown at 40 inFIG. 4B.

As noted above, where the geometric centers of the cup and the cover areboth aligned with the geometric center of the guidepiece body, theguidepiece body can swivel (tilt and rotate) about a center of rotationas shown in FIGS. 5A, 5B, 5C and 6A, 6B, 6C. For reference, in each ofFIGS. 5A, 5B, 5C the receptacle axis is in the plane of the drawing andoriented vertically on the page; and in each of FIGS. 6A, 6B, 6C thereceptacle axis is oriented perpendicularly to the plane of the drawing.In FIG. 5B the guidepiece alignment axis A is aligned with thereceptacle axis. In each of FIGS. 5A and 5C the guidepiece is tilted sothat its alignment axis (respectively, A′, A″) is unaligned with thereceptacle axis. In each of FIGS. 6A, 6B, 6C the guidepiece has beentilted in a selected direction away from the receptacle axis. The extentto which the guidepiece may be tilted is as a practical matter limitedby the shape and dimensions of the opening 34, inasmuch as theprojecting portion of the alignment tube 16 may impinge with the edge ofthe opening 34. Resistance to swiveling or rotational movement of theguidepiece within the receptacle can be increased or decreased byturning the cover in relation to the cup to tighten or loosen the inwardforce exerted by the cup and cover on the guidepiece body. At somestages during use of the apparatus, it is desirable to tighten thereceptacle so that the guidepiece is immobile under the conditions ofuse. At other stages it is desirable to loosen the receptacle enough toallow the user to tilt or rotate the guidepiece within the receptacle todirect or redirect the alignment axis in relation to features within theskull. The resistance may be finely adjusted to permit rotation and tiltof the guidepiece and yet prevent undesired movements. Portions of theinner surfaces of the receptacle and/or of the guidepiece body mayoptionally be textured to augment the frictional resistance to movementof the guidepiece.

FIGS. 7A, 7B, 7C, 7D show, in sectional view, stages in a procedure forreversibly installing the cranial access apparatus into the skull of asubject to be treated. A portion 70 of the skull is shown overlain bythe skin 71; and underlain by the intracranial contents 77 in theseFIGs.

In one stage, a hole is created in the skull, as shown at 72 in FIG. 7A.In practice, this entails the following:

Using standard neurosurgical techniques, an incision is made at theappropriate location in the subject's skull. For example, in atransfrontal approach to accessing a cerebral ventricle an incision ismade near a location on the skull known as Kocher's point.

Thereafter, using standard neurosurgical techniques, a drill hole ismade using a hand drill or other device with a drill bit size suitableto form a hole having an inside diameter D minimally larger than theouter diameter of a device that is to be advanced into the target (forexample, the cerebral ventricle). Preferably the hole diameter is largeenough to allow for some angular displacement of the particular devicethat is to be deployed through the hole. For an indwelling cerebralcatheter such as a ventricular drain or ventricular shunt, for example,a standard hole may have a diameter in a range about 6-8 mm. A drill bithaving a ¼inch (6.4 mm) size and as large as about ½ inch (12.5 mm) sizemay be suitable, for example. The diameter of the drill hole should beat least a great as the diameter of the device to be inserted throughit; for a 6 French catheter, having a nominal 3 mm diameter, a drillhole as small as about 5 mm may be suitable.

Thereafter, using standard neurosurgical techniques, the dura mater isincised. Following incision of the dura mater, if ultrasound imaging isto be employed, a small amount of a sterile, preservative-freeultrasound gel is disposed within the drill hole to allow for clearinsonation. An isotonic saline solution may be employed, but over timethe saline may disperse from the drill hole; and a gel can effectivelyserve as a matrix to support the saline in the desired region. Anexample of a suitable such gel is an ultrasound gel marketed bySonotech, Inc. under the name “UltraBio Sterile”.

In a subsequent stage, the cranial access apparatus 40 is installed inthe hole in the skull, with a result as shown in FIG. 7D. Where theapparatus is assembled prior to installation in the skull, this entailsthe following:

The assembly 40 is screwed into the hole 72, using the lower “wings” 34,34′ to rotate the assembly in a first direction (e.g., clockwise) toadvance the threads on the stem of the cup into the hole 72. Theapparatus is screwed into the hole to an extent sufficient to firmlyanchor it to the skull, while permitting eventual removal of theapparatus by rotating it the opposite way (e.g., counter-clockwise). Itmay be desirable, prior to installation of the apparatus into the skull,to screw the cover and the cap together tightly enough to inhibitmovement of the guidepiece and thereby stabilize the assembly.

As FIG. 7D shows, the apparatus provides direct access through thealignment tube lumen 19 and the stem lumen 59 and the inner portion ofthe hole 72 to features in the intracranial contents 77.

In other embodiments the cranial access apparatus may be assembled insitu, by stages illustrated in FIGS. 7B, 7C, 7D.

In a stage shown in FIG. 7B, the lower (cup) part 20 of the receptacleis screwed into the hole 72, using the lower “wings” 34, 34′ to rotatethe assembly in a first direction (e.g., clockwise) to advance thethreads on the stem of the cup into the hole 72. Either at this stage orlater the apparatus is screwed into the hole to an extent sufficient tofirmly anchor it to the skull, while permitting eventual removal of theapparatus by rotating it the opposite way (e.g., counter-clockwise).

In a subsequent stage shown in FIG. 7C, the guidepiece 10 is nested intothe cup 20 with the projecting part of the guide tube 16 directedgenerally away from the cup.

Thereafter, the cover is aligned with the cup along the receptacle axis,and the cover is screwed onto the cup, generally as described above withreference to FIGS. 4A, 4B, with a result as shown in FIG. 7D.

With either method of assembly, when ultrasound imaging is desired,sufficient sterile, preservative-free ultrasound gel is applied to thereceptacle stem and lower aspect of the guidepiece to provide adequateultrasound insonation.

The outer diameter of the receptacle stem is matched to the holediameter. For example, where the hole is made using a ¼inch diameterdrill bit, the receptacle stem is dimensioned so that the threadedportion is self-tapping when turned into the hole, resulting in a securemount of the apparatus in the hole.

Once the cranial access apparatus has been installed onto the skull ofthe subject to be treated, the apparatus can receive any of a variety ofdevices, for imaging or diagnosis or treatment, for example.

In some procedures, accurate placement of a device (such as, forexample, an intracranial catheter or similar device) in a particularsite may be required. For example, it is desirable to accurately place acatheter or similar device. Accordingly, in some embodiments cranialaccess apparatus is installed, and an imaging device is inserted in theguide tube to visualize features in the underlying intracranialcontents. The guidepiece is then swiveled to bring the alignment axisalong a path that the imaging device shows to be optimal to access aparticular treatment site. The cover and cup may thereafter be tightenedso that the guidepiece does not swivel, that is, to secure theorientation of the guidepiece alignment axis along the optimal path, andthe imaging device is withdrawn. Thereafter a device for accessing theparticular site is introduced through the secured guidepiece to thetreatment site.

FIGS. 8A and 8B show stages in insertion and use of an imaging device(in this instance, an ultrasound imaging probe) in the guidepiece ofcranial access apparatus 40 that has been installed onto the skull. Theprobe is inserted into the receiving end of the guidepiece. The probe 80includes a probe body 82 electrically connected by a cable 81 toultrasound imaging apparatus (not shown in the FIGs.). The inner surfaceof the guide tube is configured and generally dimensioned to accommodatethe shape and size of the imaging device. In the example shown here, forexample, the probe may be generally cylindrical and, accordingly, theguide tube inner surface is generally cylindrical; and the insidediameter of the tube is slightly larger than the outer diameter of theprobe. Other configurations are contemplated, as discussed below withreference, for example, to FIGS. 16A, 16B, 17A, 17B, 23A.

In one stage, the probe is inserted into the guidepiece tube. Inpractice, this entails the following:

The probe is sheathed in a standard sterile covering and brought intothe sterile surgical field.

The sheathed probe is inserted into the receiving end of the guidepiece40 and is advanced through the guide tube until the tip of the proberests at the foot of the tube. Referring to FIGS. 1A, 1B, a retainingring 14 at the foot of the tube may provide a mechanical stop foradvancement of the probe into the tube.

The selected probe may have a width (or diameter) larger than thediameter of the bore through the receptacle stem, and the guide tube isdimensioned accordingly, as is discussed below with reference to FIG.19A, for example. Any of a variety of ultrasound probes may be used, andprobes identified as being for pediatric or neonatal use may bepreferred. Suitable probes have an image width and scan depth sufficientto adequately provide location of the site of interest; for instance thesurface of the lateral ventricle is typically about 5 cm below the outertable of the skull in an adult. Examples include ultrasound transducersmarketed as the “M-series” by SonoSite, Inc., Bothell, Wash., such asfor example the model “P10x”, having a 10 mm wide linear image and a 14cm scan depth, and a larger probe housing width about 12-14 mm. Largerprobes can be accommodated within the guidepiece by providing suitablywide guidetube inner dimensions.

In a subsequent stage, the site is visualized and the optimal trajectoryand distance to the site is determined. In practice, this entails thefollowing:

The guidepiece receptacle cover is rotated about the receptacle axis inrelation to the guidepiece receptacle cup to tighten or loosen the forceon the guidepiece body, to allow the guidepiece to swivel. The imagingapparatus is started, and the guidepiece, carrying the probe, is tilteduntil the general region of the brain near the site to be accessed isvisualized. Where for example the procedure is placement of a catheterinto the lateral ventricle, the guidepiece is tilted so that theinterface of the brain and the cerebrospinal fluid of the lateralventricle is sonographically visualized. FIG. 8B shows an example of animaging procedure, in which an imaging signal 84 projects along thealignment axis A toward the target 88 within the intracranial contents.(In the stage shown here, the alignment axis of the guidepiece iscoincident with the receptacle axis.) The corresponding image appears ona display, as shown for example in FIG. 9.

Thereafter the probe is rotated within the guidepiece tube, or theguidepiece tube is rotated about the alignment axis, until thesonographic plane is approximately coronal, and then the guidepiece,carrying the probe, is swiveled until the sonographic image shows thatthe alignment axis is generally centered on the lateral ventricle.

Additional information can optionally be obtained by rotating the probewithin the guidepiece tube, or rotating the guidepiece tube about thealignment axis, until the sonographic plane is approximately sagittal,or is intermediate between coronal and sagittal.

When the optimal trajectory to the center of the lateral ventricle isidentified sonographically, the receptacle is tightened (by tighteningthe cover on the cup) to immobilize the guidepiece within thereceptacle, thereby locking the alignment axis A coincident with theoptimal trajectory.

With the guidepiece immobilized, the probe can be rotated about thealignment axis within the fixed guide tube (to view various sonographicplanes) to confirm that the selected trajectory is optimal and, if not,the receptacle can be loosened and the guidepiece can be tilted toimprove the alignment.

Once the optimal trajectory has been determined, the distance from theprobe tip to the site (in this example, the surface of the lateralventricle) is measured sonographically along the trajectory (that is,along the alignment axis). Then the imaging device is withdrawn from theguidepiece.

Once the guidepiece has been locked in place within the receptacle sothat the alignment axis is coincident with an optimal access trajectoryto the site, the apparatus can receive any of a variety of additionaldevices, depending upon the particular procedure or treatment.

Examples of such devices include ventricular catheters, needles,ventriculoscopes, ventricular shunts (such as ventriculoperitonealshunts). Such devices may typically have smaller cross-sections than theimaging device (e.g., ultrasound probe) and, accordingly, forintroduction of such a device into the guidepiece tube, an adaptor maybe provided.

An assortment of guidepiece adaptors, suitable for use in a guidepiecegenerally as described above, are illustrated by way of example in FIGS.10A, 10B, 11A, 11B, 12A, 12B. The corresponding guidepiece is shown at10 in FIG. 13. In these examples the adaptors are configured to fitwithin the guidepiece tube 16, and to receive devices having a circularcross-section that is slightly less than the inside diameter idt of theguidepiece tube. Accordingly, each of the adaptors 100, 110, 120 has acircular cross-section, with an outside diameter 105, 115, 125respectively slightly less than the inside diameter idt of thecorresponding guidepiece tube 16; and each adaptor has an inner surface107, 117, 127 defining an axial bore having a diameter ida′, ida″,ida′″, slightly greater than the outside diameter of a device to beintroduced through it. The adaptor is introduced into the receiving endof the guidepiece tube 16 and advanced to a stop. Where a stop ring 14is provided at the foot of the tube, and the adaptor is longer than (orthe same length as) the guidepiece tube, the adaptor may rest upon thering 14 at the foot of the tube. In the examples shown in these FIGs.,at one end (a receiving end) of each adaptor tube are tabs 102, 102′;112, 112′; 122, 122′ which project beyond the adaptor wall; where theadaptor is shorter than the guidepiece tube, or where a stop ring 14 isnot provided, or to provide a redundant stop function, the tabs may restupon the receiving end of the tube, preventing further advancement ofthe adaptor into the guidepiece.

For a given guidepiece a set of adaptors may be provided, all having anoutside diameter appropriate to the inside diameter of the guidepiecetube; and each having an axial bore configured and dimensioned toaccommodate a variety of particular devices. Many devices have acircular cross-section, for example, and their diameters may bestandardized.

FIGS. 14A-14E show stages in deployment of a device (in this instance, aventricular catheter) in cranial access apparatus 40 that has beeninstalled onto the skull and locked into alignment along an optimaltrajectory, generally as described above.

In one stage, the device is inserted into the guidepiece. In practice,this entails the following:

If required, an adaptor is inserted into the guidepiece, as shown inFIG. 14A. Adaptor 110 is configured and dimensioned to fit into theguidepiece tube; that is, where (as here) the guidepiece tube has acylindrical inner surface 15 the adaptor has a cylindrical outer surface115. The adaptor additionally is configured and dimensioned toaccommodate the particular device to be introduced. Where the device tobe introduced has a circular cross-section, adaptor 110 has an innersurface 117 defining an axial bore having a diameter ida slightlygreater than the outer diameter of the device. A typical ventricularcatheter, for example, may be a “9 French” catheter, having a diameterabout 3 mm; and a suitable corresponding bore diameter may be, forexample, 3.4-4.0 mm. The difference between the bore diameter and thetubing or device outer diameter for which it is intended is chosenaccording to specific needs, as greater differences allow for greaterease of passage but also allow for greater degrees of possible error inthe angle of approach to the target. For example, for a 5 cm long boreand a 3 mm wide catheter, an inner bore diameter of 3.9 mm would yield amaximum 1 degree error in the angle of approach. For a depth of targetof 10.5 cm below the top of the bore, a 1 degree error would lead to thetip of the catheter missing the optimum target by 1.8 mm, which is lessthan the diameter of the catheter and a very small fraction of the sizeof typical intracranial targets such as the ventricular system.

As FIG. 14B illustrates, the bore through the adaptor is coaxial alongthe alignment axis A of the guidepiece. Where appropriate, the catheteror device may be lubricated with a suitable sterile, preservative-freelubricant to facilitate advancement of the catheter or device throughthe bore.

In a subsequent stage, the device is inserted into the receiving end ofthe adaptor-fitted apparatus 140, as shown in FIG. 14B. In the exampleshown here, the device is a ventricular catheter 142 having a perforatedtip region 144. The tip 144 of the device is advanced through theadaptor bore to the foot of the guidepiece tube, and then into theintracranial contents 77 and a further distance toward and into thetarget site 88, as shown in FIG. 14C. The distance to which the tip isadvanced is determined by correlation with the distance from the probetip to the site, as measured during the imaging procedure. To facilitateaccurately advancing the device to the desired distance the device maybe marked with depth indicia to aid in inserting the device over thedetermined distance to the target. For example, the device may have amark at a point that is aligned with the insertion end of the adaptorwhen the device tip is at the position where the end of the probe hadbeen; this provides an indicium from which to measure proximately alongthe device the distance to which the device should be advanced. Or, forexample, the device may be marked at intervals (e.g., cm intervals) toindicate device length as measured from the tip; and the device isinserted to an indicated length that is the sum of the determineddistance to the target plus a known adaptor length. Or, both theforegoing approaches may be employed, providing additional depthaccuracy by redundancy. To simplify measuring the advance distance, itmay be preferred to dimension the adaptor such that the length of theadaptor bore is a nonfractional multiple of the intervals on the device;for example, if the indicia on the device are at cm intervals, then itmay be preferred that the adaptor bore be a nonfractional number of cmin length.

The device may be styletted, as is customary for ventricular drainplacement, to maintain stiffness and ensure that the device will proceedto and into the site along the optimal trajectory, as established by thealignment axis A of the guidepiece. Proper positioning of the catheterin the lateral ventricle may be confirmed by withdrawal of a smallamount of cerebrospinal fluid.

In a subsequent stage, the cranial access apparatus may be removed,while the intracranial device is left in place. In practice, thisentails the following:

Where the device is styletted (such as a styletted catheter), the styletcan optionally be withdrawn from the device tubing prior to removing theapparatus. A stopper 146 having an outer diameter no larger than theouter diameter of the catheter or device can be placed on the end of thecatheter or device to prevent further outflow of cerebrospinal fluid.The apparatus is disengaged from the skull by grasping the “wings” orother gripping features on the lower (cup) part of the receptacle, andturning the receptacle to unscrew it from the skull. Then the adaptorand the apparatus are withdrawn over the device, as indicated by thearrows in FIG. 14D, with a result as shown in FIG. 14E. The device 142may be held at the level of the skin or just above the proximal portionof the apparatus 140 during withdrawal of the apparatus, to preventchange in the position of the tip 144 at the site 88. Where the devicerequires, leakage of fluid outward through the device may be preventedby a stopper 146 at the end of the device opposite the tip. The stopperis narrow enough that it does not interfere with subsequent removal ofthe adaptor and the apparatus. Removal may be facilitated by withdrawingthe adaptor first and thereafter removing the guidepiece and receptacle.Removal may alternatively or additionally facilitated by sequentialremoval of the upper receptacle part 30 then the guidepiece 10, so thatthe device (for example, catheter) may be held as close as possible tothe skull during the unscrewing and withdrawal of the lower receptaclepart 20 (generally following the reverse sequence of stages illustratedin FIGS. 7A-7D.

Alternatively, where the device is styletted, the imaging apparatus maybe withdrawn over the device while the stylet is still in place in thedevice tubing. To permit withdrawal of the adaptor over the styletteddevice, the proximal end of the stylet must have no transverse dimensiongreater than the smallest inside dimension (e.g., the inside diameter)of the bore in the adaptor. Leaving the stylet in the device duringwithdrawal of the apparatus may provide additional control over thedevice, further ensuring that is does not become displaced from thetarget.

Following removal of the apparatus, customary surgical procedures may befollowed for securing the ventricular drain, for example, or forestablishing the distal aspects of a ventricular shunt. For example, asillustrated in FIG. 15, the catheter (or other device) may be tunneledsubcutaneously under a flap 153 of skin and scalp 151 such that thedistal end of the device emerges some distance away from the initialskin incision and cranial access site.

For other types of devices, such as a ventriculoscope or a needle, forexample, the apparatus may if desired be left in place while the deviceis in place, until the procedure has been carried out.

Adapters may be configured to accommodate devices having other shapes,as illustrated by way of example in FIGS. 16A, 16B, 17A, 17B. Thecorresponding guidepiece is shown at 10 in FIG. 18. In these examples,as in the examples illustrated in FIGS. 10A, 10B, 11A, 11B, 12A, 12B,the adaptors are configured to fit within the guidepiece tube 16. In theexamples shown by way of example in FIGS. 16A, 16B, 17A, 17B theadaptors are configured to receive devices having generally square(FIGS. 16A, 16B) or non-square rectangular (FIGS. 17A, 17B)cross-sections whose greatest dimensions are smaller than the insidediameter idt of the guidepiece tube. Accordingly, each of the adaptors160, 170 has a circular cross-section, with an outside diameter 165, 175respectively slightly less than the inside diameter idt of thecorresponding guidepiece tube 16. Adaptor 160 has an inner surface 167defining an axial bore having a square section, slightly larger than thesquare section of a device to be introduced through it; and adaptor 170has an inner surface 177 defining an axial bore having a rectangularsection, slightly larger than the rectangular section of a device to beintroduced through it. Adaptors may be configured to accommodate deviceshaving any of a variety of other cross-sections, such as generallytriangular, for example, or non-circular round, for example.

The adaptor is introduced into the receiving end of the guidepiece tube16 and advanced to a stop. Where a stop ring 14 is provided at the footof the tube, and the adaptor is longer than (or the same length as) theguidepiece tube, the adaptor may rest upon the ring 14 at the foot ofthe tube. In the examples shown in these FIGs., at one end (a receivingend) of each adaptor tube are tabs 162, 162′; 172, 172′ which projectbeyond the adaptor wall; where the adaptor is shorter than theguidepiece tube, or where a stop ring 14 is not provided, or to providea redundant stop function, the tabs may rest upon the receiving end ofthe tube, preventing further advancement of the adaptor into theguidepiece.

As noted above with reference to FIGS. 1A, 1B, the guide tube isdimensioned to fit a cylindrical bore through the guidepiece body. Thatis, the outer diameter of the guide tube is approximately the same asthe inner diameter of the bore. As noted above with reference to FIGS. 2and 3, the receptacle parts are dimensioned to closely embrace thecorresponding guidepiece body. As may be appreciated, guidepiece bodiesmay be dimensioned to match one (or a small number of) standardizedreceptacles. For example, there may be two standardized receptaclesdimensioned respectively for pediatric and adult use; they may differnot only in the dimensions of the stem, but also in the sphericaldiameters of the respective guidepiece bodies to be used with them. Thebore through any of such guidepiece bodies may be made large enough toaccommodate the largest device whose use in connection with theapparatus is contemplated. For use with larger imaging devices requiringlarger bore sizes, the diameter of the guidepiece ball 12 (FIG. 1A) maybe increased, with corresponding increased diameters of the innersurfaces 33 and 23 of the receptacle cover 32 and cup 22, while thediameter of the receptacle stem 27 is kept at an appropriate size foruse with a particular drill hole in the skull. Guide tubes adapted foruse with such a standardized guidepiece body may be configured anddimensioned to receive devices of a variety of shapes and sizes, andsets of interchangeable guide tubes having a specified outside diametermay provided for each standard.

Examples are shown at 190, 200, 210 in FIGS. 19A, 19B, 20A, 20B, 21A,21B. In each of these examples a guidepiece body 190, 200, 210 has astandard outside diameter 193, 203, 213, matching the inner diameter ofa standard receptacle; and each has a bore through the center defining acylindrical inner surface 191, 201, 211 and an alignment axis. A guidetube 196, 206, 216 in the bore has an outer surface (197 in FIG. 19A)having a diameter about the same as the inner diameter of the bore.

In the example of FIG. 19A, 19B, the guide tube 196 inner surface 195defines a guide tube lumen 198 having a circular cross-section largeenough to accommodate the largest device whose use in the guidepiece iscontemplated. Imaging devices (such as ultrasound probes) having largerdiameters than the drill hole in the skull can be used with such aguidepiece by selecting a guide tube having a suitable inner diameter.To accommodate smaller devices, or devices having cross-sectional shapesother than circular, various adapters configured to fit within the guidetube lumen 198 may be provided, generally as described with reference toFIGS. 10A, 10B, 11A, 11B, 12A, 12B, 16A, 16B, 17A, 17B, for example.

Or, alternatively, the bore itself in the guide tube may have anon-circular cross-section, as shown for example in FIGS. 20A, 20B, 21A,21B. For example the lumen 208 of guide tube 206 in guidepiece 200 has agenerally square cross-section, and the lumen 218 of guide tube 216 inguidepiece 210 has a generally non-square rectangular cross-section.

The inner diameter of the guide tube may be made proportionately muchlarger than the inner diameter of the stem; and the guidepiece body maybe made larger to accommodate the larger stem, as illustrated by way ofexample in FIG. 22A. The guidepiece (body 212 and guide tube 216) ishere shown rotated within the receptacle parts 222, 232. As in theexamples described above, the diameter of the hole in the skull is about¼inch, and the stem 227 is dimensioned accordingly. In this example, theguide tube inner diameter is about twice as great as the diameter of thestem lumen 259. In FIG. 22A, a large probe 282 is shown seated withinthe guide tube, and the guidepiece is shown swiveled to near the maximumaxial rotation permitted by the opening 234 in the cover 232. In thisconfiguration some portion of the image field is obscured by the loweredge 255 of the inner surface 225 of the stem 227. A resulting image isillustrated in FIG. 22B, showing the target 228 unobscured by the“shadow” 222. At this juncture the receptacle can be tightened to lockthe guidepiece 212, 216 and the probe 282 can be removed from the guidetube and replaced with an adaptor suited to receive a device to beplaced at the target. The device is then placed, and the apparatus iswithdrawn, generally as described above.

The guidepiece may be configured to accept probes having any of avariety of shapes, as well as sizes. An example is shown in FIG. 23A.Here the guidepiece (body 312 and guide tube 316) is here shown withinthe receptacle parts 322, 332. As in the examples described above, thediameter of the hole in the skull is about ¼inch, and the stem 327 isdimensioned accordingly. In this example, the guide tube is configuredto conform to an end of a particular ultrasound probe 382 andaccordingly its inner width is variable; near the foot the inner widthof the guide tube is about twice as great as the diameter of the stemlumen 359. In FIG. 23A, an irregularly shaped large probe 382 is shownseated within the guide tube, and the guidepiece is shown with its axisnearly aligned with the axis of the receptacle. In this configurationportions of the image field are obscured by the lower edge 355 of theinner surface 325 of the stem lumen 327. A resulting image isillustrated in FIG. 23B, showing the target 328 unobscured by the“shadows” 302, 302′. As may be appreciated, the guide piece (carryingthe probe) may be swiveled as described above to improve the alignmentof the axis of the device with the optimal track to the target; theresulting image will have a wider “shadow” at one side and a narrowerone at the other. At this juncture the receptacle can be tightened tolock the guidepiece 312, 316 and the probe 382 can be removed from theguide tube and, as shown in FIG. 23C, replaced with an adaptor 310suited to fit within the guide tube 316 and to receive a device 340 tobe placed at the target. The device is then placed, and the apparatus iswithdrawn, generally as described above.

Other embodiments are within the claims.

For example, as noted above the guide tube and the guidepiece body mayconstitute a single part and, in such embodiments, the guide tube lumenconstitutes the guidepiece lumen. The guide tube lumen is configured anddimensioned to receive and to maintain the position of the imagingdevice within the lumen during manipulation of the apparatus (e.g.,while swiveling the guide piece) such that the imaging device axis isaligned with the guidepiece alignment axis. And, the guide tube lumen isconfigured and dimensioned to receive and to maintain the position of anadaptor within the lumen such that the adaptor bore is aligned with theguidepiece alignment axis. Whether the guide tube and the guidepiecebody are separate parts or constitute a single part, the guide tubelumen may in some embodiments end near or flush with or inwardly fromthe outer surface of the guidepiece body, so long as the lumen providessufficiently secure alignment of the imaging device or adaptor withinit.

I claim:
 1. Apparatus for directed cranial access to an intracranialsite, comprising a guidepiece and a receptacle, wherein the receptaclecomprises a lower part and an upper part, the lower receptacle parthaving a rim and a base and a hollow stem at the base adapted to bemounted in a hole in the skull, the upper receptacle part having a rimand an opening at the top, each part of the receptacle having aninterior spherical surface, wherein the upper and lower receptacle partscan be joined at the rims to form an inner surface enclosing a generallyspherical interior; and the guidepiece comprises a body having aspherical outer surface and a lumen through the center thereof, definingan alignment axis, the guidepiece being dimensioned to fit rotatablywithin the receptacle interior, the lumen being configured anddimensioned to accept an imaging device therein.
 2. The apparatus ofclaim 1, the guidepiece body further comprising a bore through thecenter thereof, and a guide tube in the bore, wherein a lumen in theguide tube comprises the guidepiece lumen.
 3. The apparatus of claim 2wherein the guidepiece body and the guide tube are a single part.
 4. Theapparatus of claim 2 wherein the guidepiece body and the guide tube areseparate parts and the guidepiece is assembled by inserting the tubeinto the bore in the body.
 5. The apparatus of claim 2 wherein an insertend of the guide tube extends away from the body.
 6. The apparatus ofclaim 1, further comprising an adaptor insertable within the guidepiecelumen, the adaptor having an adaptor bore configured and dimensioned toaccept a device to be placed at the site.
 7. The apparatus of claim 6wherein an axis defined by the adaptor bore coincides with the alignmentaxis of the guidepiece.
 8. The apparatus of claim 4 wherein the adaptorbore is cylindrical, having a diameter at least the same as a diameterof the device to be placed at the site.
 9. The apparatus of claim 1wherein the stem is dimensioned to be mounted in a hole in the skullhaving a diameter greater than the diameter of a device to be placed atthe site, and less than about 12.5 mm.
 10. The apparatus of claim 9wherein the stem is dimensioned to be mounted in a hole in the skullhaving a diameter greater than the diameter of a device to be placed atthe site, and less than about 6.4 mm.
 11. The apparatus of claim 9wherein the stem is dimensioned to be mounted in a hole in the skullhaving a diameter greater than about 5 mm.
 12. The apparatus of claim 1wherein the stem is dimensioned to be mounted in a hole in the skullhaving a diameter in a range about 6 mm to about 8 mm.
 13. The apparatusof claim 1 wherein the imaging device comprises an ultrasound probe. 14.The apparatus of claim 1 wherein the device to be placed is dimensionedso that the adaptor through which the device was inserted is fullyremovable over the entire length thereof.
 15. The apparatus of claim 6wherein the device to be placed at the site comprises a catheter. 16.The apparatus of claim 6 wherein the intracranial site comprises acerebral ventricle, and the device to be placed at the site comprises aventricular catheter.
 17. The apparatus of claim 6 wherein the device tobe placed comprises a cerebrospinal fluid shunt.
 18. The apparatus ofclaim 6 wherein the intracranial site comprises a cerebral ventricle,and the device to be placed at the site comprises a ventricular shunt.19. The apparatus of claim 1 wherein the apparatus can be assembled byjoining the receptacle parts over the guidepiece body, an insertion endof the guidepiece lumen being situated within the top opening.
 20. Theapparatus of claim 19 wherein the rims of the receptacle parts arecomplementarily threaded, and wherein the apparatus can be assembled byscrewing the receptacle parts together over the guidepiece body.
 21. Theapparatus of claim 1 wherein the receptacle parts can be tightened onthe guidepiece body to restrict rotation of the guidepiece within thereceptacle, reversibly locking the alignment axis in relation to thereceptacle.
 22. The apparatus of claim 1 wherein an inner width of theguidepiece lumen is at least about as great as the inner diameter of thestem.
 23. The apparatus of claim 1, further comprising a stop thatprevents an imaging device inserted into the guide tube from projectinginwardly beyond the outer table of the skull.